Potential of Advanced Consolidants for the Application on Sandstone

Abstract

Alkoxy-based consolidants are widely used for conservation of cultural heritage objects made from sandstones. Even if such consolidants were introduced into practice already in the 19th century, their performance has been enhanced by several modifications to their composition only recently. To obtain a relevant comparison of their application potential, both commercial (Remmers KSE OH and SurfaPore FX SB) and a self-developed particle-modified ethyl silicate consolidant supplemented with two phosphate-based ones, were assessed. Importantly, the potential toxicity of our novel consolidants was considered. Since the stone substrate should mimic the properties of naturally weathered stone, sandstone from the Msene quarry in Central Bohemia, characterized by a high porosity and relatively low mechanical strength, is selected. From practical point of view, the long-term durability of the consolidation effect is crucial compared to the initial level of consolidation. Regarding the determination of durability of the sandstone consolidation according to an American Society for Testing and Materials (ASTM) accelerated weathering test, we performed mechanical tests in micro- (nanoindentation) and macroscale (drilling resistance measurements). The cohesion of the consolidant xerogels in the pores were determined by sorption experiments in gas phase. The durability of our TiO2 and ZnO particle-modified consolidants is superior to that of the commercial products. The aqueous diammonium hydrogen phosphate-based consolidant, which also shows exceptional durability, reveals itself to be a promising product for not only carbonate but also sandstone materials.

Freeze–Thaw and Salt Crystallization Durability of Silica Acid Ester Consolidated Porous Limestone from Hungary

“…Depending on the gel deposition rate and the deposited amount of gel in sandstone pores, the strength increase was different for KSE 100, KSE 300, and KSE 510 [38]. Modified silica acid esters seem to perform well on low strength sandstone, too [28]. This research on porous limestone consolidation is in line with previous works [23].…”

“…In our test, we used silica acid esters. The selection of the four tested materials is justified since these are the most commonly used consolidants in Hungary and commonly applied worldwide [26] for stones other than limestone, such as sandstone [27,28] or volcanic tuffs [29]. For limestone, silica acid esters are also used but in recent years, studies dealing with nano-lime treatment are also known [30][31][32].…”

Carbonate Rock Chemical Consolidation Methods: Advancement and Applications

“…We refer to rock consolidation as the strengthening of rocks by the generation of new chemical bonds between the rock grains. Alkoxysilane [Si­(OR) 4 ] products are among the most applied rock consolidants, proving efficient in sandstone grain gluing . The consolidation by these chemicals is based on the formation of amorphous silica in the rock during hydrolysis–condensation reactions .…”

“…In contrast, Graziani et al tested (applied by brushing) a mixture of TEOS with two organic bases (white spirit and isopropyl alcohol) and increased Giallo Siena and Globigerina limestone specimens’ tensile strength and dynamic modulus by 126% and 63%, respectively . Despite the consolidation efficiency of alkoxysilane products, they have several drawbacks, such as the hydrophobicity effect that lingers for a couple of months, extended curing periods which may last up to a month, and the tendency to crack with aging. ,, Moreover, Sassoni et al observed a pronounced decrease in porosity (up to 62.6%) and impairment of water sorption abilities of the rocks that were treated with TEOS . The same observations were confirmed by Graziani et al…”

“…Alkoxysilane [Si(OR) 4 ] products are among the most applied rock consolidants, proving efficient in sandstone grain gluing. 63 The consolidation by these chemicals is based on the formation of amorphous silica in the rock during hydrolysis− condensation reactions. 64 Tetraethyl orthosilicate [TEOS, Si(OC 2 H 5 ) 4 ] is the most used alkoxysilane consolidant, and its consolidation principle is based on the following reaction: 65…”